This invention relates to a rotor for an electromagnetic coupling such as an electromagnetic clutch or brake. Rotors of the same general type of that of the present invention are disclosed in Booth et al U.S. Pat. No. 5,036,964 and Brown et al U.S. Pat. No.5,125,255. The Booth et al patent also discloses one version of an electromagnetic clutch with which the rotor may be used.
A clutch rotor is made of low magnetic reluctance material and typically includes an inner hub, an axially facing disc formed integrally with and projecting radially outwardly from the hub, and an outer pole ring or flange at the outer periphery of the disc. The outer flange either defines or supports a pulley which coacts with a belt for driving the rotor. In the rotor disclosed in the Booth et al patent, the outer flange is brazed, welded or otherwise secured to the outer periphery of the disc while, in the rotor disclosed in the Brown et al patent, the outer flange is formed integrally with the outer periphery of the disc.
The electromagnetic clutch disclosed in the Booth et al clutch is a six-pole clutch which is capable of developing relatively high torque even though the clutch is comparatively compact in a radial direction. The rotor disclosed in the Brown et al patent also is for use with a six-pole clutch. Typically, a rotor for a six-pole clutch is made by forming three circumferentially extending and radially spaced rows of circumferentially spaced slots through the disc of the rotor, there being relative narrow connecting bridges between the slots of each row. The slots form air gaps of high magnetic reluctance in the disc and, when the rotor includes three radially spaced rings of air gaps, the rotor possesses the necessary magnetic characteristics to cause the clutch to be a high torque six-pole clutch.
A rotor with three radially spaced rows of circumferentially spaced slots functions adequately in many applications of the clutch. In certain high inertia applications, however, such as where the clutch is being used to drive an engine cooling fan of large diameter, the rotor is subjected to high bending forces and to high wear. Under such conditions, the comparatively weak bridges between the slots tend to shear and produce failure of the rotor.